1. Field of the Invention
This invention relates to a wrapping paper for thermosensitive recording materials. More particularly, this invention relates to a wrapping paper suitable for the diazo thermosensitive recording materials having a recording layer containing a diazonium salt, a coupling component and a coloring assistant provided on a fixable support. In the above recording layer, at least one of the diazonium salt, the coupling component and the coloring assistant is incorporated in microcapsules together with an organic solvent (except that the above three components cannot be contained in the same microcapsule).
2. Description of the Prior Art
Recently, the thermosensitive recording method has spread in the fields of facsimile and printer. As the thermosensitive recording method materials for the above recording, leuco coloring thermosensitive recording materials were employed. The leuco coloring thermosensitive recording materials are superior in color concentration and coloring rate, but they have the following problems. That is, even after recording, they are stained by coloring caused by heating or adhesion of solvents, and moreover, they are decolored by a plasticizer such as contained in cellophane adhesive tape. In order to solve these defects, diazo thermosensitive recording materials have been developed. In the recording materials, a recording layer containing a diazonium salt, a coupling component and an alkali generator or a coloring assistant is provided, and after recording, unreacted diazonium salt is decomposed by light irradiation to lose its coloring ability (Japanese Patent KOKAI Nos. 57-123086 and 57-125092). However, in such diazo thermosensitive recording materials, precoupling gradually proceeds during preservation, and undesirable fogging occasionally appears. In order to avoid this fogging, either of the coupling component or the coloring assistant is made nonpolar with waxy material (Japanese Patent KOKAI Nos. 57-4414 and 57-142636) or capsules with a hydrophobic macromolecular material (Japanese Patent KOKAI No. 57-192944) and thereby it is isolated from other components. Besides, it is also known that preservability is improved by providing a protective coat of linear polystyrene resin of which molecular weight is higher than 10,000. Particularly, fixation type diazo thermosensitive recording materials recently developed are superior because they have no such problems. The fixation type recording material has a recording layer containing a diazonium salt, a coupling component and a coloring assistant provided on a fixable support, and at least one of the above three components is incorporated in microcapsules together with an organic solvent. In the case of this fixation type recording material, microcapsules are not ruptured at the time of coloring reaction but the above reactive substances existing in and out of the microcapsules pass through the wall of the microcapsules by heating.
As the package for the thermosensitive recording materials requiring light shielding properties such as the foregoing diazo thermosensitive recording materials, the packaging materials for photographic photosensitive materials including diazo photographic photosensitive materials were usually employed. The packaging materials for photographic photosensitive materials require various properties such as light-shielding, gas barrier, moistureproofness, antistatic property, physical strengths such as breaking strength, tear strength, impact puncture strength, Gelbo test strength and wear resistance, heat sealing properties such as heat seal strength, hot tack properties (hot-seal ability) and seal ability of contraries, flatness, slipping character and the like.
Generally, it is difficult to satisfy these properties by a single material. Therefore, a single layer film of a high-pressure low-density polyethylene (LDPE) kneaded with carbon black or a pigment, or a composite laminated film composed of a LDPE film and a flexible sheet such as paper, aluminum foil or cellophane, etc. has been employed. An example of a single layer wrapping film is shown in FIG. 5. This film consists of a light-shielding LDPE film layer 5. Some examples of composite wrapping films are shown in FIGS. 6-9. The film of FIG. 6 is composed of a light-shielding LDPE film layer 5 and a flexible sheet layer 6. The film of FIG. 7 is composed of a light-shielding flexible sheet layer 7 and a LDPE film layer 8. The film of FIG. 8 is composed of a light-shielding LDPE film layer 5, a light-shielding metal foil layer 3 and a flexible sheet layer 6. They are laminated in that order, and an adhesive layer 4 is provided between each layers. The film of FIG. 9 is composed of a light-shielding paper layer 1 and a light-reflecting paper layer 2 laminated on it through an adhesive layer 4.
However, when a diazo thermosensitive recording material was coiled round the core and wrapped up in the above film, fogging caused by precoupling occasionally appears during transportation or storage.